Circuit interrupter



April 15, 1952 w. M. LEEDS ET AL 2,592,635

CIRCUIT INTERRUPTER original Filed Dec. 15, 1943 4 sheets-smelt 1 Load INVENTORS W/hf/lrop/l/. leeds, /fobe/ ff, /rf/dr/d? and Franc/'5 J Fry April 15, 1952 w. M. LEEDS ETAL 2,592,635

CIRCUIT INTERRUPTER Original Filed Dec. 15, 1945 4 Sheets-Sheet 2 4 Re.: /s rok and Franc/5J. Fry

April 15, 1952 w. M. LEEDS ET Al. 2,592,635

CIRCUIT INTERRUPTER Original Filed Dec. 15, 1945 4 Sheets-Sheet 5 F/g. a

'WITNESSES INVENTORS @Mii/f mwhrop/meef/s, /fag//fff/edf/f W 3 and #anc/5J Fry 6i BY 72/ LQVATTORNEY April 15, 1952 w. M. LEEDS ET A1. 2,592,635

CIRCUIT INTERRUPTER Original Filed Dec. 15, 1943 4 Sheets-Sheet 4 Pump sa fs Time Range t Z em Carre/7% l CE2/7fach Pau /90 (an fac 75 Op en f l Pump Sia/f5 1/0/1L ge @MMM Patented Apr. 175, 1952 UNITED STATES PATENT OFFICE CIRCUIT INTERRUPIERv Pennsylvania Continuation of application Serial No. 514,366, December'15, 1943. This application February 5, 1948, Serial No. 6,436

11 claims.Y (C1. 20o-150) This invention relates tocircuit interrupters in general, and more particularly to arc extinguishing structures therefor and is a continuation of our application Serial Number 514,366, led December 15, 1943, now abandoned.

An object of our invention is to provide an improved circuit linterrupter which utilizes a novel method for interrupting charging currents. As a result of a utilization-'01 our improved method for interrupting charging currents, We are able to interrupt high voltage circuits, such as 230 kv., with very short arcing .time employing only two are extinguishing units in a tank. By utilizing only two arc extinguishing units. there results greater simplicity of construction, and conse- Quently the rst costaud. the maintenance expense of the interrupter is reduced.

Another object of our invention is to devise an improved circuit interrupter oi the type utilizing a pressure-generating break and an interrupting break, the pressure-generating break .normally forcing fluid; under pressure toward the interrupting break to cause the interruption of load currents or short circuit currents. In our structure we utilize the interrupting ability of the pressure-generatingA breaktogether with the interrupting abilityv of .the interrupting break to eiiectthe extinction of arcs drawn during the interruption of charging currents where the amperageY involved is relatively low.

Another object is to improvise a novel method for interrupting charging currents in circuit interruptersto prevent overvoltage surges on the transmission line.

A further object is to provide an improved circuit interrupter in which a delayed uid moving means is brought into action to interrupt charging currents at a predetermined time after contact separation. This time delay shouldV fall within a time range which has precise limits and which is hereinafter disclosed.

Another object is to employ an improved delayed action piston having for its sole object the interruption of chargingv currents or like currents of a similarly low magnitude; which piston is not operative during. the interruption of either heavy load currents or short-circuit currents.

The novel method which .we disclose for interrupting charging` currents may be employed in circuit interrupters of widelyV variant construction. This method need not be connned in its use to a circuit interrupter of the type which we specifically disclose, but this novel method for interrupting charging currents may be employed on any circuit interrupter altery suitable experi- 2 mental data concerning the characteristics of such an interrupterare known.

Further objects and advantages willreadily become apparent upon a reading of the following specication taken in conjunction with. the drawings; in which:

Figure 1 is an elevational View, partly in--section, or" a circuit interruptor embodying our invention, oneuoi the insulating shields` surrounding one ci the varc extinguishing unitsbeing out away to show more clearly an elevational view oi one of the are extinguishing-units, the interrupter being shown in the closed circuit position;

Fig. 2 is an. enlarged View in vertical sectionof one ofthe arc extinguishing* units .of `jig. 1, the parts being shown in the" closedcrcuit posi-tion;

Fig. 3 isla vertical sectionaly view ofthe are extinguishing unitv shown in Fig` 2 takenrsubstantially on the line III-III of Fig. 7 with rthe `portioaabove the plate 'l1 shown in full elevation, the parts being shown during the initial portion of the circuit interrupter opening operation;

Figs; 4 through 18 show plate details which are stacked vto form'the arc extinguishing units 7;

Fig'` 19 shows a modified typeV of delayed'action piston which may be employed in place of the piston shown in Figs; 2 and 3 ;l

Fig. 20 schematically shows an'felectricalcircuit for transmitting power from suitable generating equipment across transmission lines to a suitableload circuit;

Fig. 2l is a simplied schematic diagram showing the circuit parameterspresent during the interruption of charging currents in the circuit of Fig. 20;

Fig. 22 is a simplified diagram show-ing the eircuit parametersrthat are present during the interruption'of a short circuit current vfollowing the existence of aiault;

Fig. 23 is a schematic sirnpied diagram of the circuit shown in Fig. 22 following the existence of thefault; and

Figs. 24 through 32 are curves showing the lrelation 'of thevoltage andv current during charging current and short circuit interruptions'in the circuit of Fig. 29,-assumingdifierent times for actuating the delayed action piston.

Referring to thedrawings, and more particu- `larly to Fig. 1, the reference numeral l designates a` tank filled to thelevel' 2 with a suitable arc extinguishing iluid 3, in this' instance oil. Supported by the cover 4 of thertank l are two terminal insulators 5,' 6 which enclose' terminal studs, not shown. Supported at the loWer ends of the 'supports two links 46.

3 terminal studs are two arc extinguishing units generally designated by the reference numeral 'I and which are identical in construction.

A bridging member 6 electrically connects the arc extinguishing units 'I and is reciprocally operated in a vertical direction by an insulating operating rod 9, which may be actuated by suitable operating mechanism not shown.

Referring more particularly to Fig. 2, which shows more clearly the construction of the lefthand arc extinguishing unit 'l of Fig. 1, it will be observed that a contact foot I6 is threadedly secured to the lower end of the terminal stud I I and may be clamped thereto by a bolt I2 (Fig. 1) which passes through an aperture I3 provided in the contact foot I6. The contact foot I6 supports, by means of suitable screws I4, a top dome casting I5 which forms a pressuregenerating chamber generally designated by the reference numeral I6. The pressure-generating chamber I6 has an overpressure relief valve I'i mounted on a removable inspection plate IB which may serve to vent the pressure-generating chamber I6 upon the attainment of predetermined overpressure conditions within the chamber I6.

Apertures I9 provided in the top dome casting I5 normally vent the pressure chamber I6 to the region exterior of the casting I5 and are controlled by valves 26, which are biased downwardly by suitable compression springs 2| to uncover the apertures I9. As will be explained hereinafter, following the attainment of a predetermined pressure within the pressure-generating chamber I6, the valves 2|] will overcome the biasing action of the compression springs 2| and will move upwardly to close the apertures I9.

Operable within the pressure-generating chamber I6 is a pressure-generating contact 22 which is pivotally mounted at 23 to one wall of the dome casting I5. Extending exteriorly of the dome casting I5 and serving to rotate the pressure-generating contact 22 are two actuating arms 24 having their free ends pivoted at 25 to threaded rods 26, about which are encircled compression springs 2'I. Nuts 26 are threadedly secured on the threaded rods 26 and with washers 29 form upper seats for the compression springs 2l. The lower seats for the compression springs 21 are formed by a horizontally extending metallic strip 30 having its ends slidably mounted on the rods 26 and having its central portion rigidly secured to and carried by an insulating operating rod 3|. Nuts 32 threadedly secured on the rods 26 determine the lower limit of movement of the strip 30 with respect to the rods 26.

Cooperating with the pressure-generating contact 22 to establish a pressure-generating arc, designated by the reference numeral 35 in Fig. 2, is an intermediate contact 34. Cooperable with the intermediate contact 34 to establish an interrupting arc 31 is a lower movable interrupting contact 36.

The interrupting Contact 36 has apin ,39 extending through its lower end which pivotally The two links 46 have their right ends pivoted at 4I to two links 42, the upper ends of which are pivotally mounted at '43 to fixed pivots. The operating rod 3i has an integrally formed offstanding portion 44 which serves as a lower seat for a compression -spring 45, the upper end of which is seated in a cut-out portion 46 of a lower casting plate member 41. A pin 49 extends through an elongated slot 50 formed in the offstanding portion 44. The ends of the pin 49 pass through apertures 5I formed in the two links 40 and also in two guide links 52, the left-hand ends of which, as viewed in Fig. 2, are pivotally supported at 53 to two downwardly extending support portions 54 integrally formed with the lower casting plate member 4l. The system of links is designed to restrict motion of the contact 36 to a substantially straight line direction up or down along the axis of the arc extinguishing unit '1. At the lower end of the interrupting contact 36 is threadedly secured a laterally extending member 55, at the ends of which are secured the ends of two flexible conductors 5l. The other ends of the flexible conductors 5l are connected to contact jaws 58. The contact jaws 58 are secured to the operating rod 3l by means of two threaded studs 59 about which are encircled two compression springs 66. The outer seats of the compression springs 66 are provided by nuts 6I threadedly secured on the studs 59. The conducting bridging member 8 is adapted to enter between the contact jaws 58 making electrical contact therewith and to abut against the lower end of the operating rod 3l moving the latter upwardly during the closing operation of the interrupter, The compresion springs 66 provide the contact pressure between the bridging member 8 and the contact jaws 58.

The upper portion of the insulating operating rod 3i is, as mentioned previously, rigidly secured to the metallic strip 30. Immediately above the metallic strip 36 is a washer 63 slidable on the rod 3| `which serves as a lower seat for a battery of accelerating compression springs 65. The compression springs 65 have their upper seats dened by an offstanding projection 66, in this instance integrally formed with the top dome casting I5. An aperture 61 is provided in the offstanding projection 66. Through this aperture 61 is threadedly secured a guide and piston chamber member 68 having an aperture 69 through which the upper reduced end Ill of the operating rod 3I is guided. A nut 1I is threadedly secured to the top of the portion 'I6 and serves during the opening movement of the interrupter to engage a piston member I2 movable within the piston chamber member 68 and biased upwardly against a cover 'I3 by a compression spring 'I4 encircling the :portion 'I6 of the operating rod 3|. Apertures 'I5 are provided near the lower end of the guide and piston chamber member 68, through which oil may be forced by the downward movement of the piston member 'I2 to cushion the nal portion of the opening stroke of the operating rod 3|. During the closing stroke the compression spring I4 raises the piston member 'I2 drawing oil into the piston chamber 68 through the apertures 'I5 for the next opening operation.

It will be observed that during the nal portion of the closing operation of the interrupter the battery of compression springs 65 will be compressed and the metallic strip 36 will move relative to the rods 26 compressing the compression springs 2l after the pressure-generating contact 22 has engaged the intermediate contact 34. Consequently, the compression of the compression springs 2l provides the requisite contact pressure not only between the pressure-generating contact 22 and the intermediate contact 34 but also between the intermediate contact 34 and the interrupting contact 36.

The plate structure forming the arc extinabeaee guishing unit 1 will now be described. Immediately below the top dome casting |5 is an insulating plate 11 and having a configuration more clearly shown in Figs. 4 and 5. It will be observed that the plate 11 has four apertures 18 formed therein for the reception of insulating tie rods 19 more clearly shown in Fig. 3. An aperture 80 is also provided through which passes a resistor tube 8|, the latter being employed to divide the voltage equally between the two arc extinguishing units 1 during opening and closing operations of the interrupter. A beveled aperture 82 is provided in the insulating plate 11, together with two inclined apertures 83. Immediately below the insulating plate 11 are two identical insulating plates 84 having a configuration more clearly shown in Fig. 6. The insulating plate 84 has notched portions 85 in which extend the insulating tie rods 19. rEhe plate-84 also has cut-out portions 86 and an enlarged cut-out portion B1, the purpose for which will appearY more clearly hereinafter.

Immediately below the two insulating plates 84 is an insulating plate 89 liavinga coniiguiation more clearly shown in Fig. '1. The plate 89 has notched portions 85, cut-out portions 8S, a central aperture 99, four apertures 9| adjacent to the central aperture 90 and four apertures 92, the purpose for which will appear more clearly hereinafter. Immediately below the insulating plate 89 are two insulating plates 84 having a comiguration more clearly shown in Fig. 6 and previously described. Below the two plates 84 is an insulating plate 93 having a configuration more clearly shown in Figs. 8 and 9. The plate 93 has notched portions 85, apertures 92 and a central aperture S4. Holes95 are drilled through the insulating plate 93 as shown in Fig. 8, and the outer ends of the holes 95 are threaded to threadedly receive plugs 96 (Fig. 3). The holes 95 are provided so that one may remove the threaded plugs 95 and insert a screwdriver into a hole 95 to remove a screw 91 from-the intermediate contact 34 to permit the removal of the intermediate contact 34 Without disassembling the plates forming the arc extinguishing unit 1.

Immediately below the insulating plate 93 are a plurality, in this instance three, insulating plates 99 having a conguration more clearly shown in Fig. l0. The insulating plates 99 have notched portions 85, apertures 92, cut-out portions 3S` and a central aperture |00. Immediately below the insulating plates 99l is an insulating inlet plate and having a coniiguration more clearly shown in Fig. 1l. The insulating plate |0| has apertures 18 for accommodating the insulating tie rods 19, apertures 92 and anenlarged cut-out portion |02, the purpose for which will appear more fully hereinafter.

Immediately below the insulating inlet plate |0| is an insulating orice plate |03 having a coniiguration more clearly shown in Fig. 12. The insulating orifice plate has apertures 18 to accommodate the insulating tie rods 19, cut-out portions B, apertures 92 and a central aperture |99. Immediately below the insulating orifice plate |03 is an insulating vent plate generally designated by the reference numeral |04 and shown more clearly in Fig. 13. The insulating vent plate |04 comprises two identically vformed plates |95, each of which has apertures 18 for accommodating the insulating tie rods 19, cutout portions 95 and apertures 92.v

When the two plates |05 are assembled on the insulating tie rods\19 they cooperate A'o'formf-two flared vent openings' |06l which-lead outwardly from. acent'ral' region |01' adjacent the interrupting: arc 31. immediately below the insulating venting plate |02|is an-insulating orifice plate |032 Then follows a'second insulating inlet plate |0|, an insulating orifice plate |03, an insulating vent plate |011',v aninsulating orice plate ID3,y a third-insulating inlet: platel itl, an insulating orice plate |03; an insulatingvent plate |94, an insulating: orifice plate |93 andl arfourth insulatingv inlet plate |01; Immediately below the fourth insulating inlet: plate |0| is an insulating plate. |081 having a configuration more clearly shown in Fig. 14. The insulatingplate |985 hasno-tched portions 85, apertures 92 and a central apertureV |00.

Below, the insulating plate |08. is an insulatingplate |09 havingk a conguration moreclearly showny in` Fig. l5. The insulating. plate |09 is identical to the insulating plate |08 except that there is provided a larger central. aperture ||0. Then follows a second insulating plate |08, below which is positioned an insulatingplate and having a configuration more` clearly-shown in Figs. 16 and 17. The insulating plate has a plurality, in this instance four, grooves ||2 communicating with apertures I3', the purpose for which will vappear moreclearly. hereinafter. A central aperture |00fis providedV in the insulating plate togetherwitha counterbored portion H4; the latter-serving as an upper seat for a battery of compression springs ||5 (Fig. 2). An annular:y groove ||6 is provided in the insulating plate to hold in position an insulating cylinder member 1, the purpose for which will appear more clearly hereinafter.

Immediately adjacent to the insulating plate are a plurality, in this instance ten, insulatingl plates ||8 having a conguration more clearlyshown in Fig. 18. The insulating plates H8 have notched portions 85 and an enlarged cut-out portion ||9. Adjacent the lower insulating plate ||8 is the lower casting member 41 also held in position by the insulating tie rods 19. An electrostatic shield |20k is secured to the lowencasting member 41 by anyv suitable means such as screws not shown, and the electrostatic shield |20.serves as a seat for the resistor tube 81|. Surrounding the electrotatic shield lli) and also surrounding the entire arc extinguishing unit 1 is a cylindrical member 2| composed of insulating material.V

The cylindrical member |1 denes a piston chamber generally designated by the reference numeral |22, which communicates through apertures |23 provided at the lower end of the cylindrical member ||1 to a region outside of the cylindrical member ||1 generally designated by the reference numeral |24. This region |24 communicates through the apertures 92 provided inA the several plates which collectively form four vertical flow passages generally designated by the reference numeral |25 (see Fig. 3). The upper end of the vertical flow passages |25 lead by wayl of the insulating plates 84 to the pressure-generating arc 35 (Fig. 3).

It will be observed that the grooves` |2 cooperate with the apertures ||3 provided in the insulating plate to permit the region |25 in back of the piston memberv |21 to be at practically atmospheric pressure. A compression spring |28 biases the piston member |21 downwardly. Toactu'ate the piston member |21 within the piston chamber |22 we have-provided a 7 cylindrical member |29 having an upper ilange |30, the latter serving to engage the piston member I 21 after a predetermined time 'I' and to then cause downward motion of the piston member |21 to force oil out of the piston chamber |22 through the apertures |23 into the region |24 and upwardly through the four vertical ilow passages |25 toward the pressuregenerating arc 35. A shoulder |3| integrally formed with the cylindrical member |29 serves as a lower seat for the battery of compression springs H5. An aperture |32 provided in the cylindrical member |23 serves as a guide for the interrupting contact 36. A portion |33 of the cylindrical member |23 is threaded to serve as a rack for two diametrically disposed members |34 yhaving shoulder portions |35 serving to engage the piston member |21-and to carry the latter upwardly to its charged position during the closing operation of the interrupter. rIwo set screws |31 serve to maintain the member |34 in a set `position on the rack |33 relative to the cylindrical member |29 after a proper adjustment has been made.

The lower portion of the cylindrical member |23 has two axially extending elongated notches |38 formed therein (Fig. 3) which accommodate the vertical motion of the pin 39 so that contact 36 may be moved independently of the pis- A bumper |39 threadedly secured to the end of the conducting bridging member 8 serves to actuate the cylindrical member |23 during the opening and closing operations of the interrupter.

It will be noted that the inclined apertures 83 provided in the insulating plate 11 communicate with the cut-out portions 86 provided in the several plates to form two vertical flow passages generally designated by the reference numeral |40 in Fig. 2. These two vertical iiow passages |40 communicate with eight inlet passages 4| leading toward the interrupting arc 31. The inlet passages |4| on theA same level are provided by the enlarged cut-out portion |02 formed in the insulating plates |i. Consequently, oil under pressure developed by the pressure-generating arc 35, passes downwardly through the vertical flow passages |40 through the inlet passages |4| toward the interrupting arc 31 t0 contact the interrupting arc 31 and then pass vthrough the central apertures |00 provided in the insulating orifice plates |03, to exhaust out of the ilared vent openings |06 provided in the insulating vent plate |04.

Certain aspects concerning the direction of flow of the oil from the pressure-generating arc 35 toward the interrupting arc 31 are disclosed and claimed in a patent application led Novemvber 11, 1942, Serial No. 465,244, by Leon R. Ludwig, Benjamin P. Baker, and Winthrop M. Leeds, now Patent 2,406,469, issued August 27, 1946, and assigned to the assignee of the instant application. Also certain aspects of the structure provided for maintaining the proper contact pressure between the several contacts are disclosed and claimed in the aforesaid application.

After removal of the` screw 31, the intermediate contact 34 may be removed from the arc extinguishing unit 1 through the inspection plate i3 without disassembling the unit 1. This feature is disclosed and claimed in a patent application led April 2, 1943, Serial No. 481,529, now United .States Patent 2,420,888, issued May 20, 1947, to

Winthrop M. Leeds and assigned to the assignee of the instant application.

The operation of the interrupterl will now be explained. In the closed circuit position of the interrupter, as shown by the full lines in Fig. l and in Fig. 2, the electrical circuit therethrough includes the left-hand terminal stud contact foot l0, top dome casting I5, exible conductor |42, actuating arms 24, pressure-generating contact 22, intermediate contact 34, interrupting contact 36, laterally extending portion 55, ilexible conductors 51, contact jaws 58, conducting bridging member 8 to the right-hand arc extinguishing unit 1, through which the electrical circuit passes in an identical manner to the right-hand terminal stud, not shown. When it is desired to open the electrical circuit passing through the interrupter, or in response to overload conditions existing in the electrical circuit controlled by the interrupter, suitable operating mechanism, not shown, is actuated to cause downward movement of the insulating operating rod 3. rI'he downward movement of the operating rod 9 causes downward movement of the conducting bridging member 8 and the bumper |39. The downward movement of the member 3 permits the compression spring 45 and the battery of compression springs 55 to cause downward motion of the operating rod 3|. The downward motion of the operating rod 3| causes, by

Avirtue oi the pin 49 and two links 40, downward movement of the movable interrupting contact 30. Simultaneously the downward movement of the bumper |39 permits downward motion of the cylindrical member |29, which, because of the lever action caused by the two links 40, moves at a slower downward speed than the interrupting contact 36.

During this time the piston member |21 remains stationary because the compression spring |20 is relatively weak and is not able to overcome the inertia of the oil disposed in the piston chamber 22. Also during this time the bridging member 0 remains in electrical contact with the jaws 58; in fact, the downward speed of the bridging member 8 determines the downward speed vo1" the operating rod 3|. Furthermore, during this initial downward movement of the operating rod 3| the met-allie strip 30 slides downward on the rods 26 relieving the contact pressure by permitting extension of thevcompression springs 21 until the metallic strip 30 strikes the nuts 32, at which time clockwise pivotal rotation of the pressure-generating contact 22 takes place about the pivot point 23. The net result .is a practically simultaneously drawing of both a pressure-generating arc 35 and an interrupting arc 31.

This opening motion continues until the ilange |30, moving downwardly at a speed dependent on the downward motionof the bumper |33, strikes the piston member |21, thus causing the combined biasing action of the compression spring |23 and the compression springs ||5 to bias the piston |22 downwardly. Whether the piston |21 in fact moves downwardly depends on the amperage of the current being interrupted. During the interruption of heavy load currents and short circuit currents the piston 21 will not move downwardly because of the high pressure conditions present in the pressure-generating chamber l0 which communicates with the chamber |22 under the piston |21. However, during the interruption of charging currents, light load currents, or magnetizing currents, where the amperage involved is relatively low, the piston |21 will move downwardly because of the low pressure conditions present in the pressure-generating chamber I6. Of course, the pressure conditions existent in the pressure-generating chamber IB are a function of the amperage passing through the pressure-generating arc 35.

If the interrupter is breaking a heavy load current or a short circuit current, the pressure within the pressure-generating chamber i6 will be high and the piston |21will not move downwardly, the combined biasing action of the compression springs |28, |55 not being suflicient to overcome the high pressure conditions within the pressure-generating chamber I6. In this event, the piston |21 and the cylindrical member |29 will temporarily remain stationary, or even'back up to the maximum overtravel position of the piston |21. Hence, the bumper |39 will separate from the lower end |43 of the cylindrical member |29, the interrupting contact 36, however, continuing its downward movement by virtue of thecompressionspring 45 andthe grooves |38. The rod v3| will continue to move downwardly until the nut 1| is stopped by the piston member 12 striking the member |58.

During the interruption of heavy load currents and short-circuit currents, the valves 20 will close and high pressure will exist in the pressure-generating chamber 6 because'of the high amperage passing through the pressure-generating arc 35. This high pressure-existent within the pressuregenerating chamber Iwillplace the oil disposed therein under pressure and will cause downward movement of the oil :through the two inclined apertures 83, through the 4two vertical ow passages !40, through the inlet passages Y|4| Ato contact Athe interrupting Varc 31 as the oil passes through the orifices disposed in the insulating orifice plates v|03 `to exhaust out the Vflared vent openings .|66 provided in theinsulating vent plates |04. As aresultl of thisflowof oil,`the interrupting arc 31 will be extinguished, and the electrical circuit through the interrupter will be broken. This extinguishing action takes place before the'conducting bridging member A8 Aseparates 'from the jaws 58 to move to a position indicated by the'do'tted lines in-Fig. l, thus Vintroducing two isolating gaps in the electrical circuit.

The resistortubesl having relativelyhigh resistance value are provided to divide the voltage properly across the two aro extinguishing units .1. Since the resistances of the two resistor tubes 8| are yrelatively high, theresidualcurrent passing therethrough vafter-extinction of -the arcs is relatively Vlow and of va sufficiently low value so that breakage of this residual current by the .bridging member V8 separating from lthe jaws :58

will not cause deleterious results. 'The-overpressurereliei valve I 1 limits the pressure attained in the pressure-generating chamber I6 to a -safe value.

After the interruptingprocess is completedfand after the conducting bridging member 8 lhas introduced two isolating gaps into the circuit, as

indicated by the dotted lines in Fig. 1, thefescape of gas out of the flared openings |06 vcauses a reduction of pressure within the pressure-generating chamber I6 andthe biasingiaction exerted by the compression spring |28 and thebattery of compression springs |f is suiiicientto forcethe piston member V|21 downwardly until the latter -strikesthe lower casting member 41, thus sending'a'flushing ow of oil from the piston chamber |22 through theapertures `|23 `provided `in .the cyiindrical'rnember ||1 intothe region |24, vand upwardly through the'four'vertical flow passages |25 and into the region Aadjacent the contacts 22, 34. The interruptingprocess is at this point completed. It will be observed that `the nut 1| disposed at the top of the insulating rod 3| strikes the piston member 12 to cushion the final portion of the downward opening-movement of the operating rod 3|.

The above description assumes either an interruption of heavyload currents or an interruption of short-circuit currents in which the amperage is relatively high and consequently the pressure produced in the pressure-generating chamber' l is also high. This high pressure causes a rapid flow of oil under considerable pressure toward the interrupting are 31 to quickly extinguish the same. During the interruption of charging currents, light load currents or magnetizing currents, on the other hand, the amperage involved is relatively low, say-of the -order of 50or 100 amperes, andconsequently the pressure produced inthe pressure-generating chamber YI6 is of a relatively low value. This low pressure attained in the interruption of charging currents or other light currents is not ,suflicient to effect a rapid flow of oil toward the interrupting arc 31 and consequently interruption of the interrupting arc 31 may be delayed. In interrupting charging Currentsthismay result in arc restriking and a consequent production of overvoltage. This is especially ltrue ywhere only two arc extinguishing'units 1 are provided in each phase of a transmission line for interrupting high voltages, say of the order of 230 kv.

During the interruption of charging currents, therefore, when the pressure `produced by "the pressure-generatingarc 35 is relatively low, the biasing action exerted by the compression spring |28 and the battery of compression springs I5 is sufcient to force thepiston member |21 downwardly to cause oil to flow upwardly through the vertical flow passages |25 land toward the pressure-generating arc 35. We thus take advantage oi the interrupting ability of the pressuregenerating arc 35 during the interruption of charging currents or other light currents. Furthermore, since oil is relatively incompressible the downward movement `of the piston |21 not only forces oil under pressure toward the pressure-generating arc 35 but also forces oil downwardly through the vertical Vflow passages |40, through the inlet passages |4| toward the interrupting arc 31. It will, therefore, be apparent that during the interruption of charging currents or other light currents, the downward movement of the piston member |21 permits-advantage to be taken of interrupting ability developed in both the pressure-generating gap and the interrupting gap. During'the interruption of high amperage currents,'such as heavy load currents or short-circuit currents, the effective deionization for interruption largely takes place at the interrupting arc 31. It is only during the interruption of Icharging currents, light load currents, or magnetizing currents, that interruption is greatly aided by Vdeionization in the pressure-generating arc 35.

Consequently, during the interruption of charging currents, light load currents, or magnetizing currents, at which time the piston member |21 is movable, it will be observed that there is a time delay T following separation oi' the contacts 34, 36 before the flange |30 causes downward movement of the pistonmember |21. As will bemore fully explained hereinafter the particular time delay T before the piston |21 be comes operative during the interruption of charging currents is very important. Thus, in Figs. 2 and 3 wel show a delayed acting piston which is operative only during the interruption of charging currents or other light currents, and which is not operative during the interruption of heavy load currents or short circuit currents.

In lthe delayed acting piston arrangement shown in Fig. 19, which may be used in piace of the delayed acting piston arrangement previously described, there is shown a modified type of piston member |46 movable in the piston chamber |22, there being provided a plurality of by-passing channels |41 which makes the piston ineffective in pumping oil out of the piston chamber |22 until the edge portion |48 of the piston member |46 has Ipassed the edge |40 of the cylindrical member ||1. The lower portion of the piston member |46 has a configuration identical to the lower portion of the cylindrical member |29 previously described.` Consequently, in Fig. 19, there is a time delay T 'following a contact separation before oil is forced out of the piston chamber |22 during the interruption of charging currents or other light currents. As was the case previously, the piston member |46 in Fig. 19 is inoperative during the interruption of heavy load currents or during the interruption of short circuit currents because of the-high pressure present in the pressure-generating chamber |6.

The following discussion will set forth what we believe to be the underlying theory applying tc the interruption of charging currents, and also we shall set forth the preferred time at which the piston members |46 and |21 will be operative to send fluid out of the'piston chamber |22 at a predetermined time after separation of the contact structure.

Fig. 20 schematically shows a complete electrical circuit from the generating equipment to the receiving load equipment. The generator is generally designated by the reference numeral |5| and has the neutral point grounded. The

'current then passes to a step-up transformer genu erally designated by the reference numeral |52, the primary winding being delta-connected and the secondary winding being star-connected with the neutral point grounded. The three phases ends of the three transmission lines are another set of three oil breakers |59, |55, and |6| which control the current leading to a step-down transformer generally designated by the reference numeral |62. The primary winding is star-connected with the neutral point grounded, and the secondary winding is delta-connected. The three phases |53, |64, and |65 leading from the secondary winding of the step-down transformer |62 pass through three low Voltage oil breakers |66, |51, and' |68 which control a load receiving circuit generally designated by the reference nu meral |69. The distributed capacitance between the transmission lines |56, |51, and |58 and the ground is shown as lumped into two capacitors |10 and |1| for each line.

In the interruption of charging currents, the conditions are initially such that the oil breakers |53, |54, and |55 are closed whereas the oil breakers |59, |60, |51 are open. Referring to Fig. 21

which schematically shows one vphase of such a l2 circuit, it will be observed that the generator is designated by the reference numeral i12, L represents the reactance of the generator, the oil breaker is designated by the reference numeral |53, the summation of the contact gaps of the oil breaker 53 in Fig. 20 being designated by the gap |13 in Fig, 21, and C represents the lumped distributed capacitance |10 and 11| of Fig. 20 between the transmission line |56 and the ground in Fig. 21. This capacitance C is Very large compared to the capacitor C between line and ground on the generator side of the breaker |53.

Referring to Fig. 22, we show an alternating current generator controlled by the circuit interrupter |53 feeding a reactive load |59. The cil cuit in Fig. 22 is considerably simpliiied over the more elaborate circuit shown in Fig. 20. L, as in Fig. 21, indicates the reactance of the generator |12 and C' indicates the lumped distributed capacitance in the windings of the generator and between the line |14 and the ground. With the oil breaker |53 closed (a fault not yet having occurred) a sinusoidal current passes through the load. Since the load is partly reactive the cur rent lags the generated Voltage by a small angle. If a fault occurs, as indicated in Fig. 22 by a short between the transmission line |56 and the ground, the result is a large current flow through the oil breaker |53 limited principally by inductive reactance. This large fault current will trip the breaker operating mechanism to result in the contacts of the oil breaker |53 opening. Fig. 23 schematically shows a simplied diagram of Fig. 22 after a fault has occurred and has grounded the transmission line |55. The summation of the contact gaps in the oil breaker |53 is indicated by the separation |13 in Fig. 23.

The problem of interrupting line charging currents is Very different from the problem of interrupting normal load currents or fault currents. Assume in Fig. 20 that the breakers 53, |54, and |55 are closed and that the breakers |59, |60, and |6| are open. Because of the distributed capacitance between the transmission lines |56, |51, and |58 to ground (represented by the capacitances |10, |1|) there will result a charging current passing through the breakers |53, |54, and |55 which leads the generated Voltage by approximately electrical degrees. Assume further that it is desired to open the breakers |53,

|54, and |55 to remove the voltage from the transmission lines |56, |51, and |51, and consider during such an opening operation the voltage, current and arc Voltage related with breaker |53. Fig. 21 shows a simplied circuit with C being the lumped distributed capacitance between transmission line and ground, that is, capacitance |10 plus capacitance |1| (Fig. 20), and L represents the reactance of the generator. C represents the lumped distributed capacitance in the windings of the generator |12 and between the line |14 and ground. Since C' is very small compared with` C, it may be neglected.

The reference numeral |13 indicates the summation of the contact separations in the breaker |53; for example, in Fig. 1, |13 would be the sum of the two pressure generating gaps and the two interrupting gaps for the oil breaker in Fig. 1.

Assume that the charging current passing through the breaker |53 is interrupted at the first current zero after the contacts part, as indicated in Fig. 24. In Fig. 24, |11 indicates the generated voltage, and |18 indicates the charging current passing through breaker |53 which leads the generated voltage |11 bysubstantially 90 electrical degrees because o'f the `capacitance load C. The arc voltage is representedby the reference numeral |19. At'the time indicated by the numeral |80, lthe charging current |18 passes through zero, and the circuit is broken, the voltage then existing across the contact gap |13 varying from zerorto substantially twice normal peak E, as indicated bythediference' V between the line |8| (the potential on the .line |56) and the generated voltage wave |11. The potential on the line |56 .leaks off gradually to ground, thus resulting in the negative slope ci .the line`l8l. Thus, in time the line |8| will reach zero which indicates that C is discharged; .thereafter the potential across the contact Vgap |13 will merely be the-:sinusoidal generated voltage.

Assume in Fig. ZOthatallof the breakers |53, |54, |55, |59, |60, |,6|, |66, |61 and |68 are'closed. A load current thenpasses through the breaker |53. Fig. 22 ,shows a simplified circuit of the same arrangement. Assume ,further that'a fault occurs grounding thettransmission line 156, as indicated by the fault connection Vin Fig. '22. After'the fault :has grounded the transmission line |56, a simpliiied circuit would be that'shown inFig. 23. Because the'iault current ilowing through-the .breaker V|53 is limited principally .by 4the kreactance L, it will lag the generated voltage-by substantially 90 electrical degrees. It

Vwill be observed that the-contact gap |13 .is in Fig, 26 shows the interruption of such a fault current at the first current zero after contact part. The arc vvoltage |19 across the contacts |13 attempts to assume theA generated voltagel |11 when thefault current |82 comes to zero, but overshoots because of the oscillating circuit to a theoretical amplitude of 2E assuming no damping. Finally the voltage across the contact gap |13 settles down to the generated voltage |11.

It is apparent from the above, comparing the curves in Figs..24 and 26 that the rate of dielectric build-up after current zero need be comparatively slow for charging currents, whereas the dielectricbuild-up after a fault current or a load current zero must be very rapid if the circuit is to be interrupted. Assuming the same current in either case, it is evident that with an interrupter which utilizes no pistons for ,forcing .oil into the arc region, that the break distance for interrupting thelload current should belonger than the break distance for interrupting the `charging current since the timefor the sa-me voltage diierence .to appear across the arc space is very much shorter, and. the ability tobuild up adequate .dielectric strength at this higher rate must be gained at the expense of more break distance.

the breakeris connected Isince a breakdown `on the Atransient recoveryvoltage merely results in another half .cycle of arcing, and at the next current zero, .thefsystem .conditions aiecting interruption are practically unchanged.

In the ;.interruption of charging currents, on the otherliand, *the greater dielectric ability Yat succeeding .current Yzeros can `be veryharmful to the .system :since. successiveprestrilring of the arc may build upexcessive voltage surgeson the sys- Ltem. Because :of the comparativelyv slow :rate of imposition of volta'ge across lthe Vbreaker in the case of "a 'charging current interruption, Ythe breaker 'willfstart vto interrupt the .circuit at .very short contactseparation, and, depending on the contact speed .and .interrupter characteristics, voltage will build upzuntil'the dielectric strength in the .interrupter isexceeded. This results in a restrike and an associated'transient period during which time the chargedtransmission lineis ibroughttothe Ypotential of .the generator. The deleterious effects .of Vcontinued restrilring during Aa .charging current Yinterruption are shown'in Fig. 27.

.At the 'first current izero Vthere is ra current pause, or'timeduring which the breakercurrent isizero, .but the contact gap H3 is notable to withstand .more vthan the voltage difference 1D and ya'restrike occurs, the 'breaker current Vthen building .up at |83 for another half cycle of;arc ing. .At the next `current zero'the'current pause is longer. It will ybe observed, therefore, that-the length of time of 4the'current pause is a measure Vof the ydielectric strength Aacross the contact gap |13. Since 'the'contact :gap |13 `vat the time t1,

cannot withstand the voltage difference D', a

second .restrike :occurs with Ya remainder of `a half-cycle of charging current flowing through the breaker |53. Nowthe voltage that is'trapped on ;the line |56 dueto the overswing which occurred during .the second restriking is represented by the potential |84. When the generated voltage 11 .now changes its polarityythere is im- .presseda voltage diierence ofDZacross Ythe contact .gap 13,' which, despite tthe jgreater .contact gap .and increased dielectric ability, nevertheless .breaks down at Vtime t2 to result in an overvoltage 'the tra-nsmissicn'line |58.

Fig. 29 shows the effect of continued restriking during the interruption of a shortI circuit current. Againthe reference numeral |11 repre sents the generated voltage wave, |19 the arc voltage across lthe contact gap |13, and |82 the fault current being interrupted. The arc restrikes at the first and second current zeros after contact separation because the dielectric strength of the Contact gap |13 during these two times is not suiiicient to withstand the recovery voltage. The circuit is finally interrupted at the third current zero, the dielectric strength of the contact gap |13 at this time tiybeing sufficient to withstand lthe recovery voltage transient |85 which,

1assuming no damping in the circuit of Fig. 23,

wouldswing tosubstantially 2E. When therecovery transient dies out, the voltage across the contact gap |73 is simply the generated Voltage |77.A It will be observed that there are no undesirable effects resulting from continued restriking of the fault current as'there were during continued restriking of the charging current in Fig. 27. In Fig. 27, the voltage of the system may become prohibitive if the restriking continues on the charging current interruption. From a comparison of Figs. 27 and 29, it can be seen that the interruption of charging currents is not one of just nally interrupting the circuit, but it has the additional restriction imposed that the system voltages must not become prohibitive.

There are various Ways of dealing with the problem of charging current interruptions. In a fluid lled interrupter there can be placed a great number of interrupting units in series, and by keeping the voltage per unit very low, it would be possible to interrupt the charging current with no restriking. The number of series interrupters would be very great if there were no fluid driving pistons in the interrupters. If there are fluid driving pistonsinvolved, the number of series interrupters may be small or large, depending on how the problem is approached. If the first current zero after contact separation is to be the interruption point, it is necessary to have very powerful pistons coupled with several series interrupters. As the pistons become less powerful, the number of series interrupters must increase.

The idea of a delayed piston however meets an essential requirement of our particular oil breakers, since, with our modern interrupters, only two grids per pole are necessary for fault or load current interruptions. This is true for breakers up to and including 230 kv.

Delayed action pistons have been used on interrupters for heavy load current and fault current interruptions. It was realized that if the voltage per interrupting unit is high, it is useless to pump oil with the hope of interrupting before the contacts have separated sufficiently. In order to keep the arc energy low, the pumping is delayed until an opportune time for interruption. The time to start ,pumping is, therefore, determined on the basis of lagging power factor faults.

To secure satisfactory charging current interruption it is necessary to approach the idea of delayed action from the point of view of charging currents entirely. The delay for charging current interruptions will always be less than the delay to give least are energy on short circuit lagging power factor current interruptions.

Interrupters using a self-generated oil flow from a series pressure break for short circuit interruption can have a small piston for charging current interruption adjusted for the proper delay, whereas interrupters relying on piston driven oil ow for all currents must use a compromise piston delay adjustment.

Interrupters with powerful pistons and multibreaks have been mentioned. These interrupters clear the charging' current at the rst zero after contact part practically every time. With this type interrupter no overvoltages are experienced on opening the circuit; however, the imposition of a no-overvoltage restriction on a [charging current opening is not logical since voltages of two times normal may be obtained on energizing a transmission line, while on power faults the a transient voltage may also be two times normal.

, With this in mind the requirement for an inter- 16 rupter might well contain the limitation that overvoltages be restricted to two times normal voltage.

If a restrike were to occur at the peak of the power frequency generated voltage, during a charging current interruption, that is, if the contact gap |73 broke down when the voltage V (see Fig. 24) impressed thereacross was 2E, the voltage overswing on the transmission line E56 would be 4E below the line |8| in Fig. 24 or an over- Voltage on the transmission line |56 approaching three times normal peak voltage. This is undesirable.

We have discovered that the movement of the piston member |27 in Figs. 2 and 3 should have a time delay T, or the by-passing channels M7 in Fig. 19 should be of such a length that the fluid ow out of the piston chamber |22 should be delayed to a certain time T after contact separation. This time delay T, at which fluid is forced out of the piston chamber |22 after the moment of contact separation, may fall within a particular time range hereinafter disclosed which has fairly precise limits.

The earliest limit of this time range or pumping range is 1/2 cycle before a contact separation |73 is reached sufficient to withstand double normal peak voltage (2E) applied to the contact separation l 73 for a few seconds when lled with clean oil. The delayed fluid moving means or piston must be sufficiently strong to develop substantially the full dielectric strength of the contact gap |73 at any particular contact separation in less than 1/2 cycle after pumping begins.

The latest limit of this time range or pumping range is that time in the contact stroke corresponding to a contact gap |73 at which, without pumping, restrikes during charging current interruptions take place after zero current pauses as long as 1A; cycle. This limit, however, has been found to be less critical than the earliest permissible time pumping may begin. Stated in other Words, pumping should not be delayed longer than the time required to obtain approximately Vtwice the Contact separation obtained at the earliest time pumping may begin. As was mentioned previously in connection with the cliscussion of the charging current interruption shown in Fig. 27, the length of time of the zero current pauses is a measure of the dielectric ability of the contact gap 73 and hence depends on the time after contact separation. Theoretically if a restrike occurs during a charging current interruption after 1/3 cycle zero current pause the overvoltage swing onthe transmission line |55 is twice normal peak voltage or 2E. This is not too severe a Voltage to impose on the line |56 since the amplitude of the high frequency recovery voltage transient in Figs. 26 and 29 without damping approachs 2E as shown.

Figs. 25, 28, 30,31, and 32 are all curves of charging current interruptions showing the importance of the above pumping range, and clearly indicating the undesirable results which occur if the time of initiating the iiuid flow or pumping is outside of the specied pumping range. These curves are all drawn to the same scale and the Zero point is taken at the moment of contact separation. The generated voltage is designated by the reference numeral |77. The charging current is designated bythe reference numeral |78, and the arc voltage across the contact gap |73 by the reference numeral |79. The amplitude of the line |86 designates the length of the contact gap |73.

Referring to Fig. 25, the contact gap A indicates a sepa-ration of the contacts |13, which, if lled with clean oil, can withstand 2E. The earliest point for the pumping to begin is, therefore, 1/2 cycle before this time. 25 shows the earliest time at which the pump should start pumping, and assuming that the pump does start at this earliest time the contact gap |13 or" a separation of A has a suiiciently high dielectric ability to withstand a voltage difference of 2E. Thus, the circuit is interrupted at the time t1 and the potential |81 remains on the line |55. This charge on the capacitance C gradually leaks oi so there is a slight decay of the voltage |81. rThis decay is exaggerated by the slope of the line IBi in Fig. 24. Ultimately the capacitance C is discharged and the potential across the contact gap |13 is merely the generated voltage |11.

Fig. 28 shows the effect of pumping too soon, that is the pump starts before the earliest limit of the speciiied pumping range. It is obvious that the moment of contact part bears no relation to the instantaneous current and voltage relations at this time. Current zeros may, therefore, fall anywhere within a half cycle range. Itv is assumed in Fig. 28 that a current zero falls earlier than that of Fig. 25. The iiow of oil caused by the pump helps to build up the dielectric ability of the contact gap |13, but by our assumption the contact gap |13 must be of length A at time t2 and filled with clean oil before the gap |13 can withstand 2E. Thus, the early starting of the pump in Fig 28 not only is useless but actually is harmful in that it permits a voltage difference of X to build up across the gap |13, the result being a bad restrike which imposes the high voltage |88 on the transmission line |56. A surge of charging current |89 results from this bad restrike. The reason that the voltage |88 often remains trapped on the transmission line |56 is that the voltage impressed across the contact gap |13 after the bad restrike is merely the value denoted by Y, which voltage difference the contact gap |13 may be able to withstand. When the generated voltage |11 reverses polarity to increase the voltage diierence across the contact gap |13, say to the value P at time t3, the contact gap may or may not be suiicient at this time to withstand this high voltage difference. The net result is that a high voltage is likely to be trapped on the transmission line |56 which imposes a severe electrical strain on the insulators, etc. supporting the transmission line |56.

Fig. 30 shows the latest limit of the pumping range and shows the eiects produced when the pump is started at the latest possible time. The pump is started at the end of the 1/3 cycle zero curent pause. The restrike which occurs at this time t1 results in an overvoltage swing on the transmission line |56 which is theoretically 2E, which imposition of voltage is not too severe on the system. The voltage which is finally trapped on the transmission line |56 is designated by the reference numeral ISU which is not much over normal peak voltage E. Furthermore, this voltage |90 will decay as the condenser C is gradually discharged by leakage through the insulators, etc. The momentary charging current surge caused by the restrike at t1 is designated by the reference numeral ISI.

Fig. 32 shows the eiect of pumping too late. A current zero is assumed to take place after that which is shown in Fig. 30. It is seen that the late pumping does not build up a suiiicient dielectric ability in the contact gap |13 to withstand the Cil voltage across the contact gap |13 of a value M at a time t1. A bad restrike results therefore at time t1 with a corresponding charging current surge designated by the reference numeral |92. The consequence is that a high negative voltage |93 is trapped on the transmission line |56 straining the supporting equipment.

Fig. 31 shows a charging current interruption with the pump starting at the earliest time within the specified pumping range. A current zero is assumed to take place before that taken in Fig. 25. The dielectric strength at the second current zero after Contact part is kept low by not pumping during this time (compare Fig. 28) so that even though there is a restrike still no severe overvoltage is impressed on the transmission line |56. At the third current zero, the dielectric strength of the contact gap |13 is suiiicient (the pump having started) to hold the increasing potential across the contact gap |13. It is to be observed that the time t1 of imposition of 2E across the contact gap |13 in Fig. 31 is later by the time t2 than the time ta at which the contact gap of length A is capable of withstanding 2E. Thus, interruption of the circuit is assured at time t4.

What happens if the pump starts at a time t5 within the speciiied pumping range as indicated by the arrow |94 in Fig. 31? Here again the circuit will be interrupted at t4 because a half cycle later at t1 with the contact gap |13 greater than A and with the pump having worked 1/2 cycle, the contact gap can readily withstand 2E.

We have applied our invention to an oil circuit interruptor of the type shown in Fig. 1 which controls one phase of a three-phase transmission line having a voltage of 230 kv. from line to line. That is, the voltage between say, transmission lines |56, |51, is 230 kv. The voltage from any transmission line, say, |56 to ground is 132 kv., which imposes a voltage across each arc-extinguishing unit 'I of 6 6 kv. The interruptor is a three-cycle breaker, that is, the time from the energization of the trip coil to the moment of Contact part is 1.4 cycles, and the time from the moment of contact part to the extinction of the arcs and the consequent interruption of the circuit is not over 1.6 cycles. The piston member |21 begins to move downwardly to force oil out of the piston chamber |22 during a charging current interruption when the interrupting gap is substantially 1% inches and the pressure generating gap is substantially one inch. In other words, the piston I 21 has a time lag after contact part of substantially 0.5 cycle.

From the foregoing description, it is apparent that we have discovered a new method of interrupting charging currents by utilizing a iiuid moving means or piston member which is operative only during relatively low currents and after a predetermined time T after contact part. The exact time of initiation of the fluid moving means or piston may be anywhere within the pumping range specified above.

It is clear that our method of interrupting charging currents may be applied to any type of commercial breaker after certain experimental data have been obtained taken in the absence of the pumping means. The contact gap |13 considered in the discussion is merely the summation of the several contact gaps within the breaker for interrupting one pole of the circuit. As applied to the interruptor shown in Figs. 2 and 3, the contact gap |13 is merely the sum of the two pressure-generating breaks and the two interrupting breaks.

In the interrupter embodying our invention, the fluid moving means or piston member |21 is inoperative during the interruption of heavy load currents or short-circuit currents, and is only operative during the interruption of charging currents, magnetizing currents, or relatively low load currents. The pressure produced at the pressure-generating break during the interruption of heavy load currents or short-circuit currents is sufficient to effect a rapid interruption of the interrupting arcs 31 and to effect thereby an interruption of the circuit.

The interruption of a charging current to a high-voltage transmission line is similar to opening the alternating-current charging current to a static capacitor bank. Although voltage builds up slowly at normal system frequency across the contact gap, conventional circuit breakers usually require several cycles of arcing before the double voltage peak 2E reached can be withstood by the dielectric in the contact gap. Delayed restrikes usually occur before nal interruption of the circuit, subjecting the transmission line insulation to overvoltage surges, which under certain unfavorable conditions may result in cumulative buildup to or 6 times normal voltage. It is,

` therefore, very desirable to have a circuit interrupter capable of opening charging currents either at the very first current zero after the contacts part or at least without delayed restrikes of an appreciable magnitude.

One method of eliminating restrikes is to employ a powerful oil driving piston to blast oil into a number of series contact gaps opened simultaneously. By starting the iiow of oil before the `contacts open, a sufficiently high rate of dielectric can be obtained to assure that the arc will be extinguished at the first current zero after the contacts part. The disadvantage of this scheme is the complication of the multi-break contacts and the large force necessary to provide an adequate oil blast in all of the contact gaps.

.The development of the arc extinguishing structure, the operation of which is described in the aforesaid application by Leon R. Ludwig, Benjamin P. Baker, and Winthrop M. Leeds now Patent 2,406,469, issued August 27, 1946, for high voltage oil circuit breakers has made possible high-speed interruption of short circuit currents and voltage as high as 230 kv. with but two arc extinguishing units 'l per pole. When opening charging currents, however, it has been found that with reasonable contact opening speeds the gaps opened in the first half cycle after parting contacts is insufficient in dielectric ability to withstand the double voltage peak 2E even when all arc products are completely replaced by oil using an oil iiow piston. Restrikes during such charging current operations, therefore, seemed inevitable until the problem was solved as follows: (1) Build up of dielectric in the contact gap at the rst current zero was avoided as much as possible by not pumping oil into the contact gap, and keeping the pressure within the pressure generating chamber I6 down by use of the check valve which is held open by the compression spring 2|, the latter being fairly strong. This maintenance of the check valve 20 to its open position maintains the pressure within the pressure-generating chamber I6 to a relatively low value, thereby decreasing the dielectric ability at ,both the pressure-generating gap and also the interrupting gap. This procedure prevented the possibility of a delayed restrike in the early part of the contact stroke. (2) After a predetermined contact separation was reached, and at a time within the pumping range previously speciiied, oil liow was started suddenly with sufcient pressure to close the check valve 20, and with sumcient velocity to sweep out the arc products in both the interrupting gap and the pressure-generating gap in a half cycle. Thus, at the next current zero, the elongated contact gap, completely deionized by the oil flow, was able to withstand double voltage 2E, and the circuit was opened.

As many as l5 consecutive interruptions of 45, and 180 amperes of charging current at 66,000 volts across one arc extinguishing unit 'I have been opened without delayed restriking. During the interruption of heavy load currents and during the interruption of short circuit currents, the pressure generated at the pressure-generating arc 35 is sufficient to immediately close the check valves 20 and thus to maintain a high dielectric strength within the pressure generating chamber I6.

After an interrupting operation has been completed, the rotatable pressure generating contact 22 moves to its fully open circuit position indicated by the dotted lines |95, the intermediate contact 34 is lowered to the position shown in Fig. 3, and the lower movable interrupting contact 36 is lowered to the extent that the top thereof assumes the position shown by the dotted lines |96.

From the foregoing description of our invention, it will be apparent that we have provided an improved method for interrupting charging currents utilizing improved delayed action fluid moving means, which delay falls within the interval from 1/2 cycle before the contact separation gap is of suicient length to withstand double peak normal voltage when filled with clean iiuid, and the time thereafter that the contact separation gap has increased to a length no longer than two times the length of the iirst-mentioned gap.

In the specification and in the claims the term charging curent of a transmission line may be defined as follows: The charging current of a transmission line is the current that flows into the capacitance of a transmission line when voltage is applied at its terminals.

In the specification and in the claims the term uid is intended to cover gases, liquids, vapors and sprays.

Although we have shown and described specific structures, it is to be readily apparent that the same were merely for purposes of illustration and that changes and modifications may readily be made by those skilled in the art without departing from the spirit and scope of the appended claims.

We claim as our invention:

1. In a circuit interrupter, an arc extinguishing unit, a pressure-generating contact disposed adjacent a first end of the unit and cooperable with an intermediate contact to establish a pressure generating arc adjacent the first end of the unit,

a lower movable contact movable adjacent the other or second end of the unit and cooperable with the intermediate contact to establish an interrupting arc adjacent the second end of the unit, a piston chamber disposed adjacent the second end of the unit, a piston member operable -Within the piston chamber, uid passage .means interconnecting the pressure-generating arc with the interrupting arc so -thatpressure generated 'at the former arc may be eliective'to force iiuid against the interrupting arc to effect the latters extinction, second uid passage means interconnecting the piston chamber with the pressuregenerating arc, spring means, a flange member -biased by the spring means for movement with said lower movable contact toward open circuit position, and a lost motion connection between the flange member and the piston member arranged to actuate the piston member in timed sequence with respect to the opening movementu of said lower movable contact.

2. In a circuit interrupter of the liquid immersed type for alternating current power circuits having an arcing chamber, a pair of coacting contacts and means for moving one of said contacts to establish an arc, the combination of means for interrupting predominantly capacitive current arcs comprising a piston chamber disposed adjacent one end of said arcing chamber and having communication with said arcing chamber, said movable contact extending through said piston chamber, an actuating member surrounding said movable contact and movable relative thereto, means biasing said actuating member for movement with said movable contact in the circuit opening direction, an annular piston in said piston chamber surrounding said actuating member and movable relative thereto at least during the initial portion of the opening stroke, and flange means carried by said actuating member arranged to engage said piston at a predetermined time in the opening stroke whereby said piston is moved by said biasing means during the remaining portion of the opening stroke to force liquid toward said arc and assist in extinguishing the same.

3. In a circuit interrupter, an arc extinguishing unit, a pressure-generating contact disposed adjacent a first end of the unit and cooperable with an intermediate contact to establish a pressure-generating arc adjacent the rst end of the unit, a lower movable contact movable adjacent the other or second end of the unit and cooperable with the intermediate contact to establish an interrupting arc adjacent the second end of the unit, a piston chamber disposed adjacent the second end of the unit, a piston member operable within the piston chamber, fluid passage means interconnecting the pressuregenerating arc with the interrupting arc so that pressure generated at the former aro may be effective to force fluid against the interrupting arc to effect the latters extinction, second fluid passage means interconnecting the piston chamber with the pressure-generating arc, spring means biasing the lower movable contact toward the open circuit position, a flange member movable relative to said lower movable contact, a second spring means biasing said flange member in the biased direction of said lower movable contact, and a lost motion connection between the flange member and the piston member arranged to actuate the piston member in timed sequence with respect to the opening movement of said lower movable contact only when the pressure in the region of said pressure-generating arc is below a predetermined magnitude.

4. 'I'he method of interrupting an alternating current circuit when carrying predominantly capacitance charging current which comprises, establishing one or more series arcs in the circuit, lengthening one or more of said arcs along a path into which fluid may be forced under pressure to effect deionization of the arc or arcs, delaying the start of such forced fluid flow at least to a time one-half cycle before the arc gap or gaps have attained a length sufficient to withstand double peak normal voltage under conditions cf full fluid flow, and initiating the fluid flow at aV time not later than the time at which the arc gap orgaps in the path of the injected fluid are twice the length attained at the earliest instant defined above at which the fluid flowV may be started to effect circuit interruption.

5. The method of interrupting an alternating current circuit when carryingV predominantly capacitance charging current which comprises, establishing one or more series arcs in the circuit, lengthening one or more of said arcs along a path into which liquid may be forced under pressure to effect deionization. of the. arc or arcs, delaying the start of such forced liquid flow at least to a time one-half cycle before the arc gap or gaps have attained a` length sufficient to withstand double peak, normal voltage under conditions of full liquid flow, and initiating the liquid flow at a time not later than the time at which the arc gap or gaps in the path of the injected liquid are twice the length attained at the earliest instant defined above at which the liquid flow may be started to effect circuit interruption.

6. A circuit interrupter of the liquid break type including an arc extinguishing unit, means deiining a pressure-generating chamber and an interrupting chamber, means establishing a pressure-generating arc within the pressure-generating chamber and a serially related interrupting arc within the interrupting chamber, liquid passage means interconnecting the two chambers so that liquid may flow from the pressure-generating chamber into the interrupting chamber to facilitate the extinction of the interrupting arc therein, a liquid driving piston to force liquid into one or more of the arc gaps, and delaying means to delay actuation of the piston until a time not less than one-half cycle before the sum of the arc gaps have sufficient dielectric strength under conditions of piston flow to withstand double peak normal voltage and a time not later than the time at which the arc gap or gaps in the path of the injected liquid are twice the length attained at the earliest instant dened above at which piston flow may be started.

7. A circuit interrupter of the liquid break type including means for establishing one or more series arcs in the circuit, a liquid driving piston to force liquid into one or more of the arc gaps, and delaying means to delay actuation of the piston until a time not less than one-half cycle before the sum of the arc gaps have sufficient dielectric strength under conditions of piston ow to withstand double peak normal voltage and a time not later than the time at which the arc gap or gaps in the path of the injected liquid are twice the length attained at the earliest instant defined above at which piston flow may be started.

8. A circuit interrupter of the fluid ilow type including means for establishing one or more series arcs in the circuit, uid forcing means for forcing fluid into one or more of the arc gaps. and delaying means to delay actuation of the fluid forcing means until a time not less than one-half cycle before the sum of the arc gaps have suicient dielectric strength under conditions of forced fluid flow to withstand double peak normal voltage and a time not later than the time at which the arc gap or gaps in the path of the injected fluid are twice the length attained at the earliest instant defined above at which forced fluid flow may be started.

9. A circuit interrupter of the liquid break type including means for establishing one or more series arcs in the circuit, a liquid driving piston operable only during the interruption of currents below a predetermined magnitude of the order of charging currents to force liquid into one or more of the arc gaps, and delaying means to delay actuation of the piston until a time not less than one-half cycle before the sum of the arc gaps have suicient dielectric strength under conditions of piston flow to withstand double peak normal voltage and a time not later than the time at which the arc gap or gaps in the path of the injected liquid are twice the length attained at the earliest instant defined above at which piston now may be started.

10. A circuit interrupter of the fluid iiow type including means for establishing one or more series arcs in the circuit, fluid forcing means operable only during the interruption of currents below a predetermined magnitude of the order of charging currents for forcing iiuid into one or more of the arc gaps, and delaying means to delay actuation of the uid. forcing means until a time not less than one-half cycle before the sum of the arc gaps have sufiicient dielectric strength under conditions of forced fluid flow to withstand double peak normal voltage and a time not later than the time at which the arc gap or gaps in the path of the injected fluid are twice the length attained at the earliest instant dened above at which forced fluid now may be started.

11. A circuit interrupter of the liquid break type including an arc extinguishing unit, means defining a pressure-generating chamber and an interrupting chamber, means establishing a pressure-generating arc within the pressure-generating chamber and a serially7 related interrupting arc within the interrupting chamber, liquid passage means interconnecting the two chambers so that liquid may flow from the pressure-generating chamberinto the interrupting chamber to facilitate the extinction of the interrupting arc therein, a liquid driving piston operable only during the interruption of currents below a predetermined magnitude of the order of charging currents to force liquid into one or more of the arc gaps, and delaying means to delay actuation of the piston until a time not less than one-half cycle before the sum of the arc gaps have sumcient dielectric strength under conditions of piston flow to withstand double peak normal voltage and a time not later than the time at which the arc gap or gaps in the path of the injected liquid are twice the length attained at the earliest instant dened above at which piston iiow may be started.

WINTHROP M. LEEDS.

ROBERT E. FRIEDRICH.

FRANCIS J. FRY.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date Re. 16,912 Hilliard Mar. 20, 1928 1,305,142 Mahoney May 27, 1919 1,645,288 MacNeill Oct. 11, 1927 2,025,549 Prince Dec. 24, 1935 2,258,226 Skeats Oct. 7, 1941 2,406,469 Ludwig et al Aug. 27, 1946 2,412,858 Baker et al. Dec. 17, 1946 2,420,888 Leeds May 20', 1947 2,422,569 Leeds June 17, 1947 2,424,343 Van Sickle et al. July 22, 1947 

